Semi-constrained anchoring system

ABSTRACT

Systems, devices, and associated methods for correcting spinal column deformities that help minimize a number of attachment anchors utilized for correction, facilitate use of straight or contoured rods, and/or help promote a more natural, physiologic motion of the spinal column.

BACKGROUND

Many systems have been utilized to treat spinal deformities such asscoliosis, spondylolisthesis, and a variety of others. Primary surgicalmethods for correcting a spinal deformity utilize instrumentation tocorrect the deformity as much as possible, as well as implantablehardware systems to rigidly stabilize and maintain the correction.Presently, most of these implantable hardware systems rigidly fix thespinal column or allow limited growth and/or other movement of thespinal column, to help facilitate fusion after the column has been movedto a corrected position.

SUMMARY

Some embodiments relate to systems, devices, and associated methods forcorrecting spinal column deformities that help minimize a number ofattachment anchors utilized for correction, facilitate use of straightor contoured rods, and/or help promote a more natural, physiologicmotion of the spinal column.

Some embodiments relate to a system for correcting a spinal deformitybetween a first vertebra and a second vertebra of a person's spine,where the system includes a substantially rigid rod adapted to extendacross the spinal deformity. The system also includes a first rod anchoradapted to be fixed to the first vertebra and to receive a first end ofthe rod such that the rod is allowed to translate axially relative tothe first rod anchor, as well as a second rod anchor adapted to be fixedto the second vertebra and to receive a second end of the rod. A firstforce directing member is coupled between the rod and the spinaldeformity, where the first and second rod anchors are adapted to resistlateral translation of the rod relative to the spine and to allow alongitudinal axis of the rod to change in at least a pitch and a yaw.

Some embodiments relate to exerting a distraction and/or compressiveforce on a spine by securing first and second rod anchors on a firstside of the spine. First and second portions of a rod are received inthe first and second rod anchors, respectively, such that the first andsecond portions are substantially constrained against lateraltranslation. The first and second portions are able to change in pitchand yaw at the first and second rod anchors, respectively, in responseto movement of the spine. First and second stops are located adjacentthe first rod anchor and the second rod anchor, respectively. The firstside of the spine is distracted and/or compressed by imposing a force onthe rod with the first and second stops.

This summary is not meant to be limiting in nature. While multipleembodiments are disclosed herein, still other embodiments of the presentinvention will become apparent to those skilled in the art from thefollowing detailed description, which shows and describes illustrativeembodiments of the invention. Accordingly, the drawings and detaileddescription are to be regarded as illustrative in nature and notrestrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an exemplary system for correcting a spinal deformity,according to some embodiments.

FIG. 2 is a bottom view of the system of FIG. 1 with some features notshown to facilitate understanding, according to some embodiments.

FIG. 3 shows a rod of the system of FIG. 1, according to someembodiments.

FIG. 4 shows another rod of the system of FIG. 1, according to someembodiments.

FIGS. 5a, 5b , and 6 show features of an anchor of the system of FIG. 1,according to some embodiments.

FIGS. 7 and 8 show features of another anchor of the system of FIG. 1,according to some embodiments.

FIGS. 9-11 show still another anchor of the system of FIG. 1, accordingto some embodiments.

FIG. 12 shows alternate complementary shapes for limiting roll betweenpre-selected angular limits, according to some embodiments.

FIG. 13 shows a vertebral anchor and first force directing member of thesystem of FIG. 1, according to some embodiments.

FIGS. 14a and 14b show an adjustment mechanism of the system of FIG. 1,according to some embodiments.

FIGS. 15a, 15b, and 15c show some stop features of the system of FIG. 1,according to some embodiments.

FIG. 16 is a diagrammatical view showing some of the degrees of freedomof the system of FIG. 1, according to some embodiments.

FIG. 17 is another diagrammatical view showing some other degrees offreedom of the system of FIG. 1, according to some embodiments.

FIGS. 18 and 19 are other diagrammatical views showing axial translationdegrees of freedom, according to some embodiments.

Various embodiments have been shown by way of example in the drawingsand are described in detail below. As stated above, the intention,however, is not to limit the invention by providing such examples.

DETAILED DESCRIPTION

Some embodiments relate to a system for correcting spinal deformities,as well as associated methods and devices. In general terms, the systemprovides for lateral translational corrective force(s) and/orderotational corrective force(s) on a spinal column. Some features ofthe system include highly adaptive hardware for connecting the system tothe spinal column, where the hardware facilitates a more natural rangeof motion within pre-selected limits and application of such lateraltranslational and/or derotational corrective force(s).

Various planes and associated directions are referenced in the followingdescription, including a sagittal plane defined by two axes, one drawnbetween a head (superior) and tail (inferior) of the body and one drawnbetween a back (posterior) and front (anterior) of the body; a coronalplane defined by two axes, one drawn between a center (medial) to side(lateral) of the body and one drawn between a head (superior) and tail(inferior) of the body; and a transverse plane defined by two axes, onedrawn between a back and front of the body and one drawing between acenter and side of the body. The terms pitch, roll, and yaw are alsoused, where roll generally refers to angulation, or rotation, in a firstplane through which a longitudinal axis of a body orthogonally passes(e.g., rotation about a longitudinal axis corresponding to the spinalcolumn), pitch refers to angulation, or rotation, in a second planeorthogonal to the first plane, and yaw refers to angulation, orrotation, in a third plane orthogonal to the first and second planes. Insome embodiments, pitch is angulation in the sagittal plane, yaw isangulation in the coronal plane, and roll is angulation in thetransverse plane.

In various embodiments, changes in pitch, yaw, and/or roll occurconcurrently or separately as desired. Moreover, as used herein,“lateral translation” is not limited to translation in themedial-lateral direction unless specified as such.

FIG. 1 is a perspective view of a system 10 for correcting a spinaldeformity, according to some embodiments. The system 10 includes a rod12, a plurality of rod anchors 14, including a first rod anchor 14A anda second rod anchor 14B, a plurality of vertebral anchors 18 including afirst vertebral anchor 18A and a second vertebral anchor 18B, aplurality of adjustment mechanisms 20 including a first adjustmentmechanism 20A and a second adjustment mechanism 20B, and a plurality offorce directing members 22 including a first force directing member 22Aand a second force directing member 22B. As shown, the system 10 issecured to a spinal column 24 formed of a plurality of vertebrae 26,including a first vertebra 26A, a second vertebra 26B, a third vertebra26C, and a fourth vertebra 26D.

Although the system 10 is shown with two rod anchors 14, two vertebralanchors 18, two adjustment mechanisms 20, and two force directingmembers 22, more or fewer are implemented as appropriate. For example,in some embodiments a single vertebral anchor 18 is secured to avertebra 26 at an apex of a spinal deformation or other location, with acorresponding force directing member 22 and adjustment mechanism 20coupled to such vertebral anchor 18.

As shown in FIG. 1, however, the first and second vertebral anchors 18A,18B are fixed to a portion of the spinal column 24 having an abnormalcurvature (e.g., scoliosis) in need of correction. The system 10 isoptionally used to incrementally bring the spinal column 24 to a morenatural curvature, or a single adjustment is made to the system 10 toaccomplish the desired curvature. In other embodiments, an abnormalcurvature in the spinal column 24 has been adjusted to a more naturalcurvature using other hardware, prior to or in conjunction with securingthe system 10 to the spinal column 24.

FIG. 2 shows the system 10 from a transverse plane view, with portionsof the spinal column 24 and system 10 not shown for illustrativepurposes. For reference, the rod 12, the first vertebral anchor 18A, thefirst adjustment mechanism 20A, and the first force directing member 22Aare shown along with the first vertebra 26A and third vertebra 26C.

In some embodiments, the rod 12, also described as an elongate member,is secured to the spinal column 24 at a pre-selected offset from alongitudinal axis of the spinal column 24. For example, the rod 12 isoptionally secured at an offset along a medial-lateral axis ML, orright-left axis, and anterior-posterior axis AP, or back-front axis. Insome embodiments, the rod 12 is secured on the left side of the spinalcolumn 24. As subsequently described, the offset is optionally selectedto cause at least a relative lateral translation (e.g., central ormedial movement) and derotational shift (e.g., clockwise rotation fromthe bottom view of FIG. 2) of selected vertebrae 26 of the spinal column24 (relative anterior-posterior movement of selected vertebrae 26 canalso be accomplished) such that the spinal column 24 exhibits a morenatural position.

FIG. 3 shows the rod 12 having a bend according to some embodiments. Insome embodiments, the rod 12 is substantially rigid, defining asubstantially round cross-section with a mean diameter of about 6 mm andbeing formed of a suitable biocompatible material, such as titaniumalloy ASTM F136. The rod 12 is adapted, or otherwise structured, toextend along the spinal column 24. In FIG. 1, the bend of the rod 12 isgenerally shown for illustrative purposes. In various embodiments, therod 12 is bent in one or more of the sagittal and coronal planes. Ifdesired, the rod 12 incorporates some flex, or springiness whilesubstantially rigidly retaining its shape. The rod 12 is optionallyformed of a variety of materials, including stainless steel or suitablepolymeric materials. Moreover, as subsequently described, thecross-sectional shape of the rod 12, including various portions thereof,is not limited to circular cross-sections.

As shown in FIG. 3, in some embodiments the rod 12 is contoured orangled to at least partially mimic a curvature (e.g., sagittal planekyphosis or lordosis or, alternatively, an existing, defectivecurvature, e.g., kyphosis or lordosis) of a portion of a spinal column.Although shown with a single bend, such that the rod 12 is substantiallynon-linear, in other embodiments the rod 12 includes substantiallycurved, non-linear sections, or incorporates combinations ofsubstantially bent, straight, and/or curved sections.

The rod 12 has a longitudinal axis X, as well as a first section 30, asecond section 32, and an intermediate section 34 between the first andsecond sections 30, 32. Where the rod 12 is substantially straight, thelongitudinal axis X is substantially straight. Where the rod 12 issubstantially curved or angled, the longitudinal axis X is similarlycurved or angled. The sections 30, 32, 34 of the rod 12 are optionallycontinuously formed or are formed as separate, connected parts asdesired. In some embodiments, the second section 32 and intermediatesection 34 define an inner angle Ia less than 180 degrees, for example abend angle from about 135 to about 170 degrees, although a variety ofbend angles are contemplated.

In some embodiments, at least one or both of the first and secondsections 30, 32 are generally non-round or otherwise define chasefeatures. For example, as shown in FIGS. 3 and 4, the second section 32forms at least one flat 36, the second section 32 having a substantiallyD-shaped cross-section along at least a portion thereof. In turn, thefirst section 30 and intermediate section 34 have substantially circularcross-sections, although any of the sections 30, 32, 34 optionally havenon-circular, cross-sectional shapes as desired (e.g., star-, oval-, orsquare-shaped cross-sections). As will be subsequently described, across-sectional shape of a particular section is optionally used tolimit rotation of the rod 12, although cross-sectional modifications toselectively enhance bending performance and other characteristics of therod 12 are also contemplated (e.g. I-beam, hexagonal, or other shapes).

At least some of the intermediate section 34 optionally includes asurface treatment, such as surface roughening 38 (e.g., knurling ordimpling), or other treatment (e.g., coatings, plasma treatments, orothers) for enhancing friction and/or performance. In turn, portions ofthe first and second sections 30, 32 optionally include mirror finishes,surface coatings (e.g., PTFE), or other materials or surface treatments.Though some examples have been provided, various combinations of surfacetreatments for portions of each of the sections 30, 32, 34 arecontemplated.

FIG. 4 shows a rod 12A according to some other embodiments. The rod 12Ais substantially straight, or linear, and includes any of the featuresdescribed in association with the rod 12 as appropriate. In FIG. 4features of the rod 12A similar to those of the rod 12 are designatedwith the same reference number as the rod 12 followed by an “A.”

In some embodiments, the rod 12A is of a two-piece design and includes arod adjustment mechanism 39 which provides means for increasing aneffective length of the rod 12A. The rod adjustment mechanism 39 isoptionally a female threaded sleeve adapted to extend or contract(lengthen or shorten) a gap between pieces of the rod 12A by turning theadjustment mechanism 39 to engaging threads 37 on the sleeve. Theadjustment mechanism 39 optionally has flats or other surface featuresfor receiving a tool (e.g., an open ended wrench). One example ofanother female, sleeve-type adjustment mechanism generally suitable foruse with some embodiments described herein is shown in U.S. Pat. No.4,078,559, issued Mar. 14, 1978.

Additional examples of rods in accordance with some embodiments of thesystem 10 are set forth in U.S. application Ser. No. 11/196,952, filedon Aug. 3, 2005 and entitled DEVICE AND METHOD FOR CORRECTING A SPINALDEFORMITY, as well as Ser. No. 12/134,058, filed on Jun. 5, 2008 andentitled MEDICAL DEVICE AND METHOD TO CORRECT DEFORMITY, the entirecontents of both of which are hereby incorporated by reference.

FIGS. 5a and 5b show features of the first rod anchor 14A, according tosome embodiments. As shown in FIG. 5a , the first rod anchor 14A isadapted, or otherwise structured, to be mounted, or fixed to one or morevertebrae, such as the first vertebra 26A (FIG. 1). The first rod anchor14A is further adapted to receive, and includes means for receiving, therod 12 such that the rod 12 is secured laterally, against lateraltranslation relative to the first rod anchor 14A. In some embodiments,the rod 12 is substantially prevented from translating in a directionsubstantially perpendicular to the longitudinal axis X at the firstpoint P1. In turn, the rod 12 (shown in cut-away) is able to slideaxially, or translate axially, along the longitudinal axis X, relativeto the first rod anchor 14A through a first pivot point P1. The rod 12is also able to change in pitch, yaw, and roll about the first pivotpoint P1.

The first rod anchor 14A is optionally formed of biocompatible metallicmaterials, such as titanium, stainless steel, and/or biocompatiblepolymeric materials, such as PEEK and/or composite materials. In someembodiments, and as shown in FIG. 5a , the first rod anchor 14A includesa single-piece housing 40 having receptacle portion 48 adapted, orotherwise structured, to receive the rod 12. The first rod anchor 14Afurther includes a mounting portion 50 adapted to secure the first rodanchor 14A to one or more vertebrae, such as the first vertebra 26A andan additional vertebra 26 above or below the first vertebra. In otherembodiments, the mounting portion 50 is secured to a single vertebra,such as the first vertebra 26A (e.g., laterally across the firstvertebra 26A at the pedicles, or at a single point—such as a singlepedicle—on the first vertebra 26A.

As subsequently described, in some embodiments, the housing 40 is of amulti-piece design (e.g., as shown in FIGS. 7-11).

In some embodiments, the mounting portion 50, also described as a plate,is adapted to be secured at two or more points, for example spanningbetween two vertebrae (e.g., the L3-L4 vertebrae) or spanning across aportion of a single vertebra (e.g., pedicle-to-pedicle on a singlevertebra).

FIG. 5b shows the receptacle portion 48 in cross-section. According tovarious embodiments, the receptacle portion 48 is generally ring-shapedand forms a passage 52 having a revolute, convex surface 54 having anupper curve 56 and a lower curve 58. The receptacle portion 48 isadapted to allow the rod 12 to pass through the passage 52 at the firstpivot point P1, where the passage 52 defines a minimum effectivediameter (e.g., providing appropriate clearance between the rod 12 andreceptacle portion 48) that allows the rod 12 to slide through passage52. The passage 52 also allows the rod 12 to rotate and angulate aboutthe longitudinal axis X at the first pivot point P1 while minimizinglateral translation or inhibiting substantial lateral translation. In atleast this manner, the rod 12 is able to rotate and angulate about thelongitudinal axis X at the first pivot point while lateral translationof the rod 12 with respect to the receptacle portion 28 is substantiallylimited in all planes. In alternate terms, the rod 12 is able to slidewithin the passage 52 and change in yaw, pitch, and roll at the firstpivot point P1, while being constrained from side-to-side movementwithin the passage 52 at the first pivot point P1.

In some embodiments, the mounting portion 50 includes a stem 60 and apedestal 62, the pedestal 62 having an central portion 64, a firstanchor point 66, and a second anchor point 68, the central portion 64extending between the first and second anchor points 66, 68 and each ofthe anchor points 66, 68 defining a surface suitable for mounting thefirst rod anchor 14A to one or more vertebrae 26. The first and secondanchor points 66, 68 optionally include through holes 70, 72,respectively, for receiving a fastener (not shown), such as a pediclescrew or similar device to secure the mounting portion 50 to one or morevertebra 26, such as the first vertebra 26A (FIG. 1).

In some embodiments, the first rod anchor 14A is adapted, or otherwisestructured, to limit pitch and yaw of the rod 12 to a predefined range.For example, the rod 12 is able to angulate within a range untilopposing surfaces of the rod 12, contact, or bind with the upper andlower curves 56, 58 of the convex surface 54. In other words, a radiusof curvature of the convex surface 54 is optionally selected to controla range of motion of the rod 12. In some embodiments, pitch and yaw ofthe rod 12 is limited to within an angular range Ra of about 60 degrees,for example. As subsequently described in association with the secondrod anchor 14B, various means of limiting roll and/or sliding of the rod12 within a predefined range are also contemplated.

Although in some embodiments the mounting portion 50 is adapted toreceive one or more fasteners as shown in FIGS. 5a and 5b , FIG. 6 showsthe first rod anchor 14A with the mounting portion 50 being adapted toact as a fastener, similar to that of a pedicle screw. Thus, the firstrod anchor 14 a optionally includes fastener means for securing thefirst anchor 14A to one of the vertebra 26.

Although FIGS. 5a, 5b , and 6 are illustrative of some potentialfeatures the system 10, FIGS. 7 and 8 show a first rod anchor 114Aaccording to some other embodiments, where FIG. 7 is a perspective viewwith the rod 12 received by the first rod anchor 114A and FIG. 8 is across-sectional view of the first rod anchor 114A with the rod 12removed. The first rod anchor 114A is substantially similar to the firstrod anchor 14A, although a housing 140 of the first rod anchor 114Aincludes a receptacle portion 148A and a sleeve portion 148B. In someembodiments, the sleeve portion 148B is substantially spherical in shapeand the receptacle portion 148A forms a substantially spherical matingrace for the sleeve portion 148B.

As shown in FIG. 8, the receptacle portion 148A has a revolute,substantially concave surface 154A and the sleeve portion 148B has arevolute, substantially convex surface 154B. The surfaces 154A, 154B areadapted, or otherwise structured, to form a substantially complementaryfit with one another, such that the sleeve portion 148B is captured bythe receptacle portion 148A and is allowed relative rotational andangular movement with respect to the receptacle portion 148A.

The sleeve portion 148B has a passage 152 defining a pivot point P11through which the rod 12 is able to be slidably received. As with otherembodiments, the complementary relationship between the sleeve portion148B and the receptacle portion 148A is optionally designed to restrict,or limit, certain relative movement of the rod 12 with respect to thefirst rod anchor 114A. For example, in some embodiments, pitch and yawof the rod 12 about the pivot point P11 is limited when opposingsurfaces of the rod 12 contact the receptacle portion 148A proximate afront 156 and/or a back 158 of the receptacle portion 148A.

FIG. 9 is a perspective view of the second rod anchor 14B and FIGS. 10and 11 are perspective views of portions thereof. The second rod anchor14B is adapted to be fixed, and provides means for fixation to a secondvertebra, such as a second vertebra 26B (FIG. 1). The second rod anchor14B is further adapted to receive, and provides means for receiving therod 12 (FIG. 1) such that the second rod anchor 14B limits translationalmovement of the rod 12 except along the longitudinal axis X and allowsthe rod 12 to change in at least pitch and yaw about a second pivotpoint P2. The second rod anchor 14B is optionally substantially similarto the first rod anchor 14A or first rod anchor 114A, including anydesired combination of previously-described features.

The second rod anchor 14B is optionally formed of biocompatible metallicmaterials, such as titanium or stainless steel and/or biocompatiblepolymeric materials, such as PEEK. In some embodiments, and as shown inFIG. 9, the second rod anchor 14B includes a housing 200 havingreceptacle portion 202 and a sleeve portion 204 adapted to receive therod 12, the second rod anchor 14B further including a mounting portion(e.g., similar to the mounting portion 50 of the first rod anchor 14A)adapted to secure the second rod anchor 14B to the second vertebra 26B.

The second rod anchor 14B is optionally adapted, or otherwisestructured, to limit rotation, or roll, of the rod 12 about thelongitudinal axis X of the rod 12 (FIG. 3). In particular, the secondrod anchor 14B provides means for allowing the rod 12 to angulatewithout substantial lateral translation relative to the second rodanchor 14B or substantial rotation about the longitudinal axis X. Thesleeve portion 204 is optionally spherical in shape and the receptacleportion 202 forms a substantially spherical mating race, where rotationof the sleeve portion 204 relative to the receptacle portion 202 issubstantially inhibited in at least one plane.

FIG. 10 shows the receptacle portion 202 and FIG. 11 shows the sleeveportion 204, where the receptacle portion 202 has a revolute,substantially concave inner surface 210 and the sleeve portion 204 has arevolute, substantially convex outer surface 212. The surfaces 210, 212are adapted to form a substantially complementary fit with one another,such that the sleeve portion 204 is captured by the receptacle portion202 and is allowed relative angular movement with respect to thereceptacle portion 202.

As shown in FIG. 10, the receptacle portion 202 also includes a pair ofprotrusions 216 (e.g., pins), extending inwardly from and at oppositesides of the inner surface 210. In turn, as shown in FIG. 11, the sleeveportion 204 has a circumferential groove 218 adapted to slidably receivethe protrusions 216 and an internal passage 220 through which the rod 12is able to be slidably received. A pivot point P2 is also defined in thepassage 220, the rod 12 passing through the pivot point P2.

The passage 220 optionally has a non-circular cross-section (e.g., asubstantially D-shaped cross-section corresponding to the second section32 of the rod 12). Upon mating the non-circular cross-sections of therod 12 and the passage 220, rotation of the rod 12 relative to thesleeve portion 204 is substantially inhibited.

Upon slidably receiving the protrusions 216 in the circumferentialgroove 218 the pitch and yaw of the rod 12 are able to change. Relativerotation between the sleeve portion 204 and the receptacle portion 202,however, is substantially inhibited. Thus, as relative rotation betweenthe sleeve portion 204 and the receptacle portion 202 is alsosubstantially inhibited, relative rotation between the rod 12 and thesecond rod anchor 14B is substantially inhibited or limited, allowingthe rod 12 to be maintained at a pre-selected rotational positionrelative to the second rod anchor 14B. It also should be understood thatother cross-sectional shapes for each of the passage 220 and rod 12 canbe selected to allow some degree of rotation about the longitudinal axisX within a predefined range, including, for example, that shown in FIG.12, where the rod 12 is shown with features allowing rotation up to astop 220A formed by the sleeve 204. The cross-sectional shape of the rod12 is also optionally selected to limit axial translation of the rod 12as desired.

As with other embodiments, the second rod anchor 14B is also optionallyadapted to restrict, or limit angulation of the rod 12 (e.g., pitch andyaw) with respect to the second rod anchor 14B. For example, pitch andyaw of the rod 12 about the pivot point P2 is limited when the rod 12contacts the receptacle portion 202 proximate a front 222 and/or a back224 of the receptacle portion 202. A size and shape of the receptacleand/or sleeve portions 202, 204 is selected to define such limit(s) asdesired.

FIG. 13 shows the first vertebral anchor 18A and first force directingmember 22A from a front elevation view. The first vertebral anchor 18A,also described as an anchor arm, is adapted to be fixed, and providesmeans for fixation, to a third vertebra 26C (FIG. 1). As previouslydescribed, the first vertebral anchor 18A is fixed to a portion of thespinal column 24 (FIG. 1) having an abnormal curvature in need ofcorrection.

The first and second vertebral anchors 18A, 18B are optionallysubstantially similar, and thus various features of both the first andsecond vertebral anchors 18A, 18B are described in association with thefirst vertebral anchor 18A, where when referenced, features of the firstvertebral anchor 18A are designated with reference numbers followed byan “A” and similar features of the second vertebral anchor 18B aredesignated with similar reference numbers followed by a “B.”

The first vertebral anchor 18A includes an arm 250A and a head 252A. Insome embodiments, the arm 250A extends from the head 252A to a terminalend 254A and is disposed generally perpendicular to the head 252A. Thearm 250A is optionally rotatable relative to the head 252B and isadapted to extend across a portion of the third vertebra 26C, forexample, from one side of the spinal column 24 to an opposite side ofthe spinal column 24. For example, the first vertebral anchor 18A issecured to the third vertebra 26C such that the arm 250A extends acrossthe third vertebra 26C through a hole or hollowed portion in the spinousprocesses (not shown) of the third vertebra 26C.

The head 252A is adapted, or is otherwise structured, to be fixed to aportion of the third vertebra 26C, such as a pedicle of the thirdvertebra 26C. The head 252A optionally includes and/or is adapted towork in conjunction with any of a variety of structures capable ofengaging the third vertebra 26C. For example, the first vertebral anchor18A optionally includes a pedicle screw 256A secured through the head252A to a pedicle of the third vertebra 26C.

The first force directing member 22A is secured to the first vertebralanchor 18A at an appropriate location on the first vertebral anchor 18A.For example, in some embodiments the first force directing member 22A issecured to the first vertebral anchor 18A at least at the terminal end254A of the arm 250A such that the first force directing member 22Aextends from the terminal end 254A of the arm 250A.

Additional examples of vertebral anchors (also described as “implants”)in accordance with some embodiments of the system 10 are set forth inU.S. application Ser. No. 11/196,952, filed on Aug. 3, 2005 and entitledDEVICE AND METHOD FOR CORRECTING A SPINAL DEFORMITY, as well as Ser. No.12/134,058, filed on Jun. 5, 2008 and entitled MEDICAL DEVICE AND METHODTO CORRECT DEFORMITY, the entire contents of both of which are herebyincorporated by reference.

FIGS. 14a and 14b show the first adjustment mechanism 20A, where FIG.14b shows the first adjustment mechanism 20A with a portion removed toillustrate inner features thereof. In some embodiments, the firstadjustment mechanism 20A provides means for securing the first forcedirecting member 22A to the rod 12. In some embodiments, the firstadjustment mechanism 20A, also described as a tensioner or coupler, isfurther adapted to adjust, and provides means for adjusting a length ofthe first force directing member 22A. The first and second adjustmentmechanisms 20A, 20B are optionally substantially similar. Thus, variousfeatures of both the first and second adjustment mechanisms 20A, 20B aredescribed in association with the first adjustment mechanism 20A, wherefeatures of the first adjustment mechanism 20A are designated withreference numbers followed by an “A” and similar features of the secondadjustment mechanism 20B are designated with the same reference numbersfollowed by a “B.”

In some embodiments, the first adjustment mechanism 20A includes a reel260A, a circumferential gear 262A surrounding the reel 260A, a verticalgear 264A in contact with the circumferential gear 262A, an actuationhead 268A, and a housing 270A.

The reel 260A, as well as the circumferential gear 260A and verticalgear 264A are maintained at least partially within the housing 270A. Inturn, the housing 270A is adapted to be secured to the rod 12. Forexample, the housing 270A optionally forms a central lumen through whichthe rod 12 is receivable. Upon inserting the rod 12 through the centrallumen, the housing 270A is adapted to be clamped onto the rod 12.

In some embodiments, the housing 270A incorporates a clamshell design(e.g., a first portion adjustably secured to a second portion) adaptedto be tightened onto the rod 12 (e.g., using one or more fasteners).Thus, in some embodiments, the first adjustment mechanism 20A issubstantially fixed with respect to the rod 12. In other embodiments,however, the first adjustment mechanism 20A is movable with respect tothe rod 12, for example being able to rotate about the rod 12.

The first force directing member 22A is attached or secured to the reel260A and passes out of the housing 270A through an appropriately sizedopening in the housing 270A. Actuation of the vertical gear 264A via theactuation head 266A turns the circumferential gear 262A, which turns thereel 260A, thus winding (or unwinding, depending on the direction inwhich the reel 260A is turned) the first force directing member 22Aabout the reel 260A. Rotation of the reel 260A in the appropriatedirection draws the first force directing member 22A in toward the firstadjustment mechanism 20A, pulling the first vertebral anchor 18A (FIG.13) toward the first adjustment mechanism 20A according to some methodsof correcting a spinal defect.

Additional examples of adjustment members (also described as “adjustmentmechanisms”), in accordance with some embodiments of the system 10 areset forth in U.S. application Ser. No. 11/196,952, filed on Aug. 3, 2005and entitled DEVICE AND METHOD FOR CORRECTING A SPINAL DEFORMITY, aswell as Ser. No. 12/134,058, filed on Jun. 5, 2008 and entitled MEDICALDEVICE AND METHOD TO CORRECT DEFORMITY, the entire contents of both ofwhich are hereby incorporated by reference.

As shown in FIGS. 13 and 14, the first and second force directingmembers 22A, 22B are optionally substantially similar, and thus variousfeatures of both the first and second force directing members 22A, 22Bare described in association with the first force directing member 22A,where features of the first force directing member 22A are designatedwith reference numbers followed by an “A” and similar features of thesecond force directing member 22B are designated with similar referencenumbers followed by a “B.”

In some embodiments, the first force directing member 22A issubstantially flexible such that the first force directing member 22A isable to be pivoted in a multiple directions and/or be spooled or wound,for example. Suitable flexible materials for forming the first forcedirecting member 22A include wire and stranded cables, monofilamentpolymer materials, multifilament polymer materials, multifilament carbonor ceramic fibers, and others. In some embodiments, the first forcedirecting member 22A is formed of stainless steel or titanium wire orcable, although a variety of materials are contemplated.

The first force directing member 22A, also described as a connector orcable, is adapted to be secured to the first vertebral anchor 18A andthe first adjustment member 20A, the force directing member 22A definingan effective length between the first adjustment mechanism 20A and thefirst vertebral anchor 18A, and thus the rod 12 (although, in someembodiments, the first force directing member 22A is secured directly tothe rod 12). As described, in some embodiments, the first adjustmentmechanism 20A is adapted to modify, and provides means for modifying,the effective length of the force directing member 22A. The first forcedirecting member 22A has a body 280A and extends from a first end 282Ato a second end 284A.

FIG. 1 shows the assembled system 10. In some embodiments, assembly ofthe system 10 includes securing the first and second force directingmembers 22A, 22B to the first and second vertebral anchors 18A, 18B,respectively. The first and second force directing members 22A, 22B arealso secured to the first and second adjustment mechanisms 20A, 20B. Thefirst and second adjustment mechanisms 20A, 20B are secured to the rod12. The first and second rod anchors 14A, 14B are secured to the firstand second vertebrae 26A, 26B, respectively. The rod 12 is received inthe first and second rod anchors 14A, 14B to secure the rod 12 againstlateral translation relative to the spinal column 24. The first andsecond vertebral anchors 18A, 18B are secured to the third and fourthvertebrae 26C, 26D. Upon assembly of the system 10, the first and secondadjustment mechanisms 20A, 20B are adjusted as desired to pull the firstand second vertebral anchors 18A, 18B toward the first and secondadjustment mechanisms 20A, 20B, and thus the rod 12.

The first force directing member 22A is assembled to the first vertebralanchor 18A by securing the first end 282A of the first force directingmember 22A to the first vertebral anchor 18A proximate the terminal end254A thereof. In some embodiments, the first force directing member 22Ais secured at the terminal end 254A of the first vertebral anchor 18A,and extends along at least a portion of the arm 250A to the head 252A,although the first force directing member 22A is attached at anylocation along the arm 250A and/or the head 252A of the first vertebralanchor 18A as appropriate. The first force directing member 22A issecurable to the first vertebral anchor 18A via a variety of methods,including welding, adhesives, tying, and/or screw fixation, for example.

The second force directing member 22B and the second vertebral anchor18B are optionally secured or connected together using similarapproaches.

As previously described, the first force directing member 22A extends tothe first adjustment mechanism 20A, enters the housing 250A, and iswound about the reel 260A, thereby coupling the first adjustmentmechanism 20A to the first vertebral anchor 18A as well as the rod 12.In some embodiments, the first force directing member 22A is secured tothe reel 260A via welding, screw fixation, adhesives, and/or issufficiently wound about the reel 260A for frictional retention of thefirst force directing member 22A on the reel 260A.

The second force directing member 22A and the second adjustmentmechanism 20B are optionally secured or connected together using similarapproaches.

The rod 12 is received by the housings 40, 200 of the first and secondrod anchors 14A, 14B, respectively. Features of the first and second rodanchors 14A, 14B are selected to limit pitch, yaw, roll, and axialsliding of the rod 12 as desired.

The rod 12 is secured against lateral translation relative to thelongitudinal axis of the spinal column 14 by securing the first andsecond rod anchors 14A, 14B to at least the first and second vertebra26A, 26B, respectively. The first rod anchor 14A is secured to at leastthe first vertebra 26A, for example by screwing the first rod anchor 14Ato the first vertebra 26A (e.g., at or near the transverse processes)using one or more pedicle screws. The second rod anchor 14B is similarlysecured to at least the second vertebra 26B. The first rod anchor 14Aand/or the second rod anchor 14B are optionally secured to multiplevertebrae 26 for enhanced stability.

In some embodiments, the rod 12 is attached by the rod anchors 14A, 14Bto transverse processes on the left side of the spinal column 24 and isable to slide axially relative to the first and/or second rod anchors14A, 14B. In other embodiments, the rod 12 is attached by the rodanchors 14A, 14B to the right side of the spinal column 24, on differentsides of the spinal column 24 (e.g., the first rod anchor 14A on theleft side and the second rod anchor 14B on the right side), or along themid-line of the spinal column 24. In other embodiments, the rod 12 isadjustable length to compensate for changes in length of the spinalcolumn 24. Regardless, the interaction between the rod 12 and the firstand second rod anchors 14A, 14B helps facilitate growth and more naturalmovement of the spinal column 24.

FIGS. 15a, 15b, and 15c show various stop features 286 for limitingaxial sliding, or translation of the rod 12 relative to a rod anchor,such as the first rod anchor 14A. Generally, sliding of the rod 12 in aparticular axial direction is substantially limited, or arrested, when astop feature 286 engages, or abuts an adjacent rod anchor 14.

As shown in FIG. 15a , the rod 12 optionally includes a narrowed portion286 a received in the first rod anchor 14A with wider, adjacent portions286 b of the rod 12 limiting axial sliding of the rod 12. As shown,although axial sliding of the rod 12 is substantially prevented bylocating the stop features 286 adjacent the first rod anchor 14A, thereis still some tolerance allowed, or play, as appropriate in the fitbetween the wider portions 286 b of the rod 12 and the first rod anchor14A.

As shown in FIG. 15b , the system 10 optionally includes stops 286 c, orcollars, that are fit onto the rod 12 adjacent the first rod anchor 14Ato substantially limit axial sliding of the rod 12 within the first rodanchor 14A. In some embodiments, the stops 286 c are metal or polymericcollars crimped onto the rod 12, although a variety of designs andmethods of securing are employed as desired. As shown, although axialsliding of the rod 12 is substantially prevented with respect to thefirst rod anchor 14A, there is still some limited play or slop asappropriate in the fit between the rod 12 and the stops 286 c.

As shown in FIG. 15c , the system 10 optionally utilizes both a stop 286c and a narrowed portion 286 a with a wider portion 286 b to limit axialsliding of the rod 12 relative to the first rod anchor 14A within adesired range of motion. For example, as shown in FIG. 15c , the stop286 c is located toward an end of the rod 12 on one side of the firstrod anchor 14A and the wider portion 286 b is located on the other sideof the first rod anchor 14A with a desired spacing between the stop 286c and the wider portion 286 b. Any combination of stop features 286 andspacing are implemented as appropriate.

FIG. 16 is a diagrammatical view of a system 10A similar to that of FIG.1, where FIG. 16 illustrates various degrees of freedom of the rod 12 atthe first and second rod anchors 14A, 14B, according to someembodiments. As shown, the system 10A further includes a third vertebralanchor 18C secured to a fifth vertebra 26D. The third vertebral anchoris substantially similar to the first and/or second vertebral anchors18A, 18B. The system 10 also optionally includes a corresponding thirdforce directing member 22C, e.g., a cable or wire, and a thirdadjustment mechanism 20C. Although adjustment mechanisms 20 includingmeans for adjusting the effective length of the force directing members22 have been described, in some embodiments one or more of theadjustment mechanisms 20 acts as a means for coupling a correspondingforce directing member to the rod 12 without incorporating suchadjustment features. For example, the third adjustment mechanism 20C, orany of the adjustment mechanisms described herein, is optionally a crimpor fastener means for securing the force directing member 22C to the rod12 (e.g., a clamp or crimp).

The rod 12 is bent (e.g., as shown in FIG. 3) and, as designated by thedirectional arrows, is free to change in pitch, yaw, and roll, as wellas to slide axially along the longitudinal axis X at the first rodanchor 14A (and thus, at the first pivot point P1) and is free to changein pitch and yaw at the second rod anchor 14B while relative changes inroll and axial sliding are substantially limited or substantiallyprevented at the second rod anchor 14B (and thus, at the second pivotpoint P2). In some embodiments, collars 288A or other stop features(such as those previously described) are located on the rod 12 (e.g.,crimped onto the rod 12) on either side of the second rod anchor 14B inorder to inhibit sliding movement of the rod 12. In turn, a stop feature288B (such as one of those previously described) is located proximate aterminus of the rod 12 in order to help prevent the rod 12 from slippingoff the first rod anchor 14A.

The interaction between the vertebral anchors 18A, 18B, adjustmentmechanisms 20A, 20B, and in particular the flexible nature of theirrespective coupling through use of the force directing members 22A, 22Ballows the system 10 to move dynamically with the spinal column 24,while exerting and/or maintaining a corrective force (e.g., lateral andderotational forces) on the third and fourth vertebrae 26C, 26D. Inother words, the system 10 is semi-constrained, providing a lateral andderotational anchor point while facilitating at least some degree ofnatural movement in the spinal column 24.

Moreover, by limiting rotation, or roll, of the rod 12, the bend in therod 12 is oriented and maintained in a desired rotational position.Maintaining the rotational orientation at one end (i.e., at the secondrod anchor 14B) is useful, for example, to help ensure that the bend orshape of the rod 12 consistently follows or otherwise appropriatelytracks a desired curvature of a spinal column 24. Freedom of rotation atthe other end of the rod 12 (i.e., at the first rod anchor 14A),however, still permits the spinal column 24 to have more naturalmovement while the corrective forces are being applied.

Thus, according to various embodiments, the spinal column 24 (and thus,the person) is able to twist, bend side-to-side, and bendforward-and-backward in a more natural manner while corrective forcesare being applied to the spinal column 24. In some embodiments, theeffective lengths of the force directing members 22A, 22B are adjusted(e.g., periodically or all at one time), bringing the spinal column intonatural alignment, while the system 10 still facilitates a more naturalmovement of the spinal column 24 (e.g., twisting and bendingforward-and-backward and side-to-side) due to the freedom of movementafforded by the system 10.

FIG. 17 is a diagrammatical view of a system 10B illustrating variousdegrees of freedom of the rod 112 at the first rod anchor 14A and asecond rod anchor 290 substantially similar to the first rod anchor 14A,according to some other embodiments of the system 10. With the system10B, the rod 112 is substantially straight (FIG. 4) and, as designatedby the directional arrows, is free to change in pitch, yaw, and roll, aswell as to slide axially along the longitudinal axis X, at each of thefirst and second rod anchors 14A, 290.

In some embodiments, each of the first and second rod anchors 14A, 290shown generally in FIG. 16 are substantially the same as the first rodanchor 14A shown in FIGS. 5a and 5b , for example. In other embodiments,each of the first and second rod anchors 14A, 290 are substantially thesame as the first rod anchor 114A shown in FIGS. 7 and 8, although anycombination of the previously-described anchor features described inassociation with any of the rod anchors 14A, 114A, 14B are contemplated.

The rod 112 also optionally includes stop features 300, such as the stopfeatures 286 previously described, to help prevent the rod 112 fromslipping out of the first and second rod anchors 14A, 290. In thismanner, the rod 112 is able to slide axially, along the longitudinalaxis X (FIG. 4) until one of the stop features 300 contacts one of thefirst and second rod anchors 14A, 290. Once again, the system 10Bprovides dynamic adjustment and movement with the spine, while exertinga corrective force (e.g., translational and derotational forces) on thevertebrae 26 (e.g., the third and fourth vertebrae 24C, 24D).

FIGS. 18 and 19 show systems 10C, 10D, respectively, demonstratingvariations in axial rod constraint according to some embodiments. Thesystems 10C, 10D are each shown including a first rod anchor 360 and asecond rod anchor 370 which incorporate features of any of the anchorspreviously described. The axial arrows indicate freedom of movement ofthe associated rods, although a designation of degrees of freedom inpitch, yaw, and roll at the anchors 360, 370 are left from FIGS. 18 and19 for ease of illustration. Various degrees of freedom at the anchors360, 370 are incorporated as appropriate.

As shown in FIG. 18, the system 10C includes a rod 375 (e.g., similar tothe rod 12A) including a rod adjustment mechanism 376 (e.g., similar tothe rod adjustment mechanism 39), a first stop feature 380A, a secondstop feature 380B, and a third stop feature 380C, the stop features380A, 380B, 380C being secured to and/or formed with the rod 375 (e.g.,similar to the stop features being similar to any of the stop features286 previously described).

The rod 375 is substantially constrained against axial sliding by thesecond and third stop features 380B, 380C at the second rod anchor 370and is allowed some axial sliding, or axial translation, outwardly awayfrom the first stop feature 380A. In some embodiments, the stop features286 and the first and second rod anchors 360, 370 provide means forimposing a distraction force on the spinal column 24 and/or for limitingcompression of the spinal column 24 along one or more sides of thespinal column 24 (e.g., left, right, anterior, and/or posterior sides).

In some embodiments, the rod adjustment mechanism 376 is used to apply adistraction force by expanding an effective length of the rod 375 suchthat the first and second stop features 380A, 380B engage the first andsecond rod anchors 360, 370 resulting in a compressive force on the rod375 that the rod 375 substantially rigidly resists. The compressiveforce on the rod 375, in turn, results in a distraction, or elongationforce on a side of the spinal column 24 to which the anchors 360, 370 ofthe system 10C are coupled. Moreover, the stop features additionally oralternatively provide a limit on compression of the spinal column 24 atthe first side of the spinal column 24 by limiting relative movement ofthe anchors 36, 370 toward one another on the rod 375.

Although the rod 375 of the system 10C is placed under a compressiveload, the rod 375 is able to move axially in a first direction, e.g., toallow further distraction and/or natural movement—e.g., such that thespinal column 24 (and thus, the person) is able to twist, bendside-to-side, and bend forward-and-backward in a more natural mannerwhile distractive forces are being applied to the spinal column 24. Inturn, axial movement of the rod 375 in a second direction generallyopposite the first direction is limited (e.g., thereby limitingcompression of the spinal column 24 beyond the axial limit set by thestop features 286). Moreover, although the system 10C is described asapplying a distraction force and/or compressive limit to one side of thespinal column 24, in other embodiments a distraction force is applied toboth sides of the spinal column 24, to an anterior side of the spinalcolumn 24, to a posterior side of the spinal column 24, or combinationsthereof.

As shown in FIG. 19, the system 10D includes a rod 400 (e.g., similar tothe rod 12A) including a rod adjustment mechanism 402 (e.g., similar torod adjustment mechanism 39), a first stop feature 410A and a secondstop feature 410B, the stop features 410A, 410B being secured to and/orformed with the rod 400 (e.g., similar to any of the stop features 286previously described). The rod 400 is substantially constrained againstaxial sliding and/or outward expansion by the first and second stopfeatures 410A, 410B, the stop features 41A, 410B providing means forimposing a compressive force on the spinal column 24 and/or for limitingdistraction of the spinal column 24 along one or more sides of thespinal column 24 (e.g., left, right, anterior, and/or posterior sides).In some embodiments, the rod adjustment mechanism 402 is used to apply acontraction or tensioning force on the spinal column to which the system10D is coupled by contracting or shortening the rod 400 using theadjustment mechanism 402 such that the first and second stop features410A, 410B engage the first and second rod anchors 360, 370 to apply acompressive force to the spinal column (not shown).

Although the rod 400 of the system 10D is placed under a tensile load,the rod 400 is able to move axially in a first direction, for example,to allow further compression of the spinal column 24 (and thus, theperson) is able to twist, bend side-to-side, and bendforward-and-backward in a more natural manner while compressive forcesare being applied to the spinal column 24. Axial movement of the rod 400is still substantially limited in a second direction generally oppositethe first direction, for example, limiting distraction of the spinalcolumn 24 beyond the axial limit set by the stop features 286. Moreover,although the system 10D is described as applying a compressive forceand/or distraction limit to one side of the spinal column 24, in otherembodiments a tensile, or compressive force is applied to both sides ofthe spinal column 24, to an anterior side of the spinal column 24, to aposterior side of the spinal column 24, or combinations thereof. Infurther embodiments, the system 10D can apply a compressive force and/ordistraction limit to one side of the spinal column 24, while the system10C applies a distraction force and/or compression limit to the oppositeside of the spinal column 24.

In view of the foregoing, systems, methods, and devices according to thevarious embodiments provided herein help minimize a number of anchorpoints utilized for correction, facilitate use of straight or contouredrods, and/or help promote a more natural, physiologic motion of thespinal column 24 during or after correction of the deformity.

Various modifications and additions can be made to the exemplaryembodiments discussed without departing from the scope of the presentinvention. For example, while the embodiments described above refer toparticular features, the scope of this invention also includesembodiments having different combinations of features and embodimentsthat do not include all of the described features. Accordingly, thescope of the present invention is intended to embrace all suchalternatives, modifications, and variations as fall within the scope ofthe claims, together with all equivalents thereof.

What is claimed is:
 1. A rod anchor for correcting a spinal deformitycomprising: a mounting portion configured to secure the rod anchor to afirst bony element; and a ring-shaped receptacle portion unitarilyformed with the mounting portion, the ring shaped portion having arevolute convex inner surface defining a passage, the passage having alongitudinal axis passing through a center of the passage and configuredto allow a rod received therethrough to pivot in pitch and yaw about apivot point at a center of the passage while being constrained fromlaterally translating towards the revolute convex inner surface, whereinthe mounting portion includes a pedestal having a longitudinal axisextending in a direction parallel to the longitudinal axis of thepassage, the longitudinal axis of the pedestal being laterally offsetfrom the longitudinal axis of the passage, the pedestal having a centeraligned with a center of the receptacle portion.
 2. The rod anchoraccording to claim 1, wherein the revolute convex inner surface isconfigured to allow a rod received therethrough to slide longitudinallywithin the passage.
 3. The rod anchor according to claim 1, wherein therevolute convex inner surface is configured to allow a rod receivedtherethrough to roll about the pivot point.
 4. The rod anchor accordingto claim 1, wherein the receptacle portion is of unitary construction.5. The rod anchor according to claim 1, wherein the mounting portionincludes a stem extending from an outside surface of the receptacleportion and that is transverse to the passage and to the pedestalportion.
 6. The rod anchor according to claim 5, wherein the pedestalcomprises a plate attached to the stem, the plate defining a first holeconfigured to receive a fastener to secure the plate to a first bonyelement.
 7. The rod anchor according to claim 6, wherein the platedefines a second hole configured to receive a fastener to secure theplate to a second bony element such that the plate spans the first andsecond bony elements.
 8. The rod anchor according to claim 6, whereinthe plate defines a second hole configured to receive a fastener tosecure the plate to the first bony element.
 9. A rod anchor forcorrecting a spinal deformity comprising: a mounting portion configuredto secure the rod anchor to a first bony element; and a ring-shapedreceptacle portion fixed relative to and unitary with the mountingportion, the receptacle portion defining a passage, the passage having alongitudinal axis passing through a center of the passage, the passagedefined by a revolute convex inner surface of the ring-shaped receptacleportion configured to allow a rod received therethrough to pivot inpitch and yaw about the longitudinal axis while being constrained fromlaterally translating relative to the longitudinal axis, wherein themounting portion includes a pedestal having a longitudinal axisextending in a direction parallel to the longitudinal axis of thepassage, wherein the mounting portion includes a stem extending from alateral outside surface of the receptacle portion and that is transverseto the passage and to the pedestal, the stem having a center alignedwith a center of the pedestal.
 10. The rod anchor according to claim 9,wherein the receptacle portion is of unitary construction.
 11. The rodanchor according to claim 9, wherein the pedestal comprises a plateattached to the stem, the plate defining a first hole configured toreceive a fastener to secure the plate to a first bony element.
 12. Therod anchor according to claim 11, wherein the plate defines a secondhole configured to receive a fastener to secure the plate to a secondbony element such that the plate spans the first and second bonyelements.
 13. The rod anchor according to claim 11, wherein the platedefines a second hole configured to receive a fastener to secure theplate to the first bony element.
 14. A rod anchor for correcting aspinal deformity comprising: a mounting portion configured to secure therod anchor to a first bony element; and a ring-shaped receptacle portionof unitary construction with the mounting portion having a revoluteconvex inner surface defining a passage, the passage having alongitudinal axis passing through a center of the passage, the passageconfigured to allow a rod received therethrough to pivot in pitch andyaw about the longitudinal axis while being constrained from laterallytranslating relative to the longitudinal axis, wherein the mountingportion includes a stem extending from an outside surface of thereceptacle portion and transverse to the longitudinal axis and apedestal extending transverse to the stem and having a longitudinal axisextending parallel to the longitudinal axis of the passage such that thelongitudinal axis of the pedestal is laterally offset from thelongitudinal axis of the passage, wherein center points of thereceptacle portion, stem and pedestal are aligned.
 15. The rod anchoraccording to claim 14, wherein the pedestal comprises a plate attachedto the stem, the plate defining a first hole configured to receive afastener to secure the plate to a first bony element.